1. Field of Invention
This invention relates to mechanical guns and projectors, specifically to such guns and projectors in which fluid pressure is provided by the user's mouth or lungs. This invention also relates generally to a sabot projectile; more particularly, a sabot projectile suited for use even at low operating pressures such as those provided by human breath.
2. Introduction
The inventive apparatus and method for launching subcaliber projectiles which is adapted to perform efficiently and smoothly at propellant operating pressures that include the range of pressures that may be supplied by the breath of a human user. Furthermore, in certain embodiments the discarding of the associated sabot means features a very quick, clean separation from the subcaliber projectile, with sabot discarding fully operational at projectile velocities that include the range of velocities attainable by projectiles launched by the breath of a human user from a blowgun. Thus the instant invention is especially well-suited for providing a blowgun which can utilize the breath of the user to efficiently and accurately launch subcaliber projectiles.
Before moving further into this disclosure, it should be noted that the term, full caliber, when used herein to refer to blowgun projectiles, may be understood to mean, essentially full caliber, or, substantially full caliber, in order to include the many examples of full caliber blowgun projectiles met with in practical usage which have an actual caliber or diameter which is slightly less than the caliber of the barrel bore, in order that the widest portion of the projectile may substantially slidingly seal with the barrel bore to prevent excessive leakage of pressurized air or breath during launch, yet slide through the bore without excessive friction or snugness of fit, in order to achieve efficient propulsion. Thus a broadening of the meaning of the term, full caliber, to be inclusive of all three possibilities of projectiles with actual caliber dimension equal to, slightly greater than, or slightly less than the caliber dimension of the barrel bore, applies to the fullness of this disclosure, and will be understood to also apply to information set forth herein concerning the dimensions of full caliber sabot means employed with subcaliber blowgun projectiles.
It will be seen that the instant invention makes possible, in certain embodiments, appropriately low levels of launching resistance of the associated sabot projectile assembly, and appropriately low or very low levels of discarding resistance of the associated sabot means, thereby making the efficient and accurate launching of subcaliber projectiles compatible with the relatively low operating pressures provided by a human user's breath, and with the relatively modest velocities and energies typically attained by blowgun projectiles accelerated by the user's breath.
3. Prior Art
Blowguns work in a known manner to utilize the user's breath to accelerate and launch a projectile. Blowgun performance may be improved by increasing accuracy, power, and range, which is generally accomplished by broad strategies such as increasing launch force or velocity of the projectile, or by modifying the balance characteristics and aerodynamic properties of the projectile. Other broad strategies for improving blowgun performance include providing increased ease of aiming, as with a sighting mechanism, and providing a blowgun which can function as a multi-shot repeater, with the convenience and increased rate of fire compensating in a certain measure for any deficiencies of accuracy or power.
The prior state of the art regarding blowguns and improvements to their performance may be generally established by the following cited patents: U.S. Pat. No. 186,651 to Luther C. White and U.S. Pat. No. 856,813 to John Schultz utilized tapered bores with cooperating compressible dart pistons to provide increased launch force. U.S. Pat. No. 344,915 to Lewis H. Lang & John W. Hart utilized an interior annular shoulder detent in cooperation with a compressible dart piston so as to impose a temporary acceleration delay to boost launch force. U.S. Pat. No. 4,419,978 to Loftus utilized a pultruded barrel construction to facilitate proportioning of the bore for a longer power stroke to increase launch velocity. U.S. Pat. No. 6,588,413 to Yoichi Nagasue utilized an offset mouthpiece to allow sighting alignment of one eye directly along the blowgun barrel instead of the typical offset alignment of the eye when the barrel is aligned directly with the user's mouth. Taking a different approach, U.S. Pat. No. 4,565,009 to Porter utilized a stereoscopic blowgun sighting apparatus which exploits the user's binocular vision to create an illusionistic overlay image for superimposed sighting alignment with the target, suitable for use with a barrel aligned directly with the mouth. U.S. Pat. No. 3,137,287 to Rufo D. De Arbun and U.S. Pat. No. 3,124,119 to Carl Ayala provided repeating blowguns that launched elongate projectiles. U.S. Pat. No. 2,888,003 to Swanson and U.S. Pat. No. 5,850,826 to Guthrie provided repeater blowguns with tubular magazines that launched spherical projectiles. U.S. Pat. No. 5,544,642 to Guthrie provided a revolver-type repeater blowgun that selectively launched spherical or elongate projectiles.
The above cited patents are generally relevant to the prior state of the art. The following patents are more specifically related, each having partial relevance to one or more aspects of the inventive blowgun. U.S. Pat. No. 873,628 to Charles E. Stivers utilized a conical paper dart piston for improved bore sealing properties. U.S. Pat. No. 4,283,061 to Rolf W. Jordan utilized a dart in which the tapered shaft and light weight of the hollow impeller piston yield a forwardly disposed center of gravity to promote aerodynamic stability of the projectile. Perhaps closest to the instant invention are the immediately following four blowgun-related patents: U.S. Pat. No. 3,735,748 to Gaylord utilized a blowgun having a plurality of magnets to hold darts on the barrel for easy access, with one magnet also holding a dart partially loaded within the barrel bore. U.S. Pat. No. 2,679,838 to Thompson utilized a projectile retaining blowgun which may be considered to include a type of projectile detent. U.S. Pat. No. 4,103,893 to Walker provided a tranquilizer dart especially suited for a blowgun, designed for launch with a sabot described implicitly in the method of use. U.S. Pat. No. 632,838 to Jacobs provided a blowgun that launched subcaliber spherical shot from a blowgun via a full caliber projectile carrier that was retained in the blowgun bore after launch. However, unlike the instant invention, none of these patents described or contemplated embodiments or alternative embodiments which utilized an external magnetic detent or other type of external detent means to assist in locating one or more elements of a sabot projectile assembly within the blowgun bore pending launch acceleration.
U.S. Pat. No. 3,735,748 to Gaylord may be considered to use a type of projectile detent, a magnet mounted near the mouthpiece which may serve to hold a dart partially loaded within the barrel bore. However, it is clearly the intention that the detent should only hold the dart in place within the bore in a partially loaded position, rather than in a fully loaded position. Furthermore, Gaylord does not disclose or contemplate alternative embodiments or methods of use in which such a projectile detent is used to help locate elements of a sabot projectile assembly within the bore and in spatial relation to one another.
U.S. Pat. No. 2,679,838 to Thompson provided a projectile retaining blowgun in the form of a peashooter with a hole in the barrel for partial insertion of the user's fingertip, which together with an interior annular shoulder provided by the mouthpiece, may be considered to function as a type of projectile detent with elements that cooperate in mutual opposition to locate or confine a full caliber projectile within the bore prior to launch and to prevent premature projectile displacement toward the breech or toward the muzzle. However, like Gaylord, Thompson does not disclose alternative embodiments or methods of use in which such a projectile detent is used to locate one or more elements of a sabot projectile assembly. Furthermore, Thompson's type of fingertip detent, although an elegant solution for the peashooter and projectile he discloses, would not be generally applicable to a wide variety of types of blowgun projectiles, particularly certain types of sabot projectiles that include subcaliber projectiles.
Although U.S. Pat. No. 4,103,893, to Walker does not recite or illustrate a sabot as a numbered element, a sabot is implicit in the disclosed method of use, which mentions launching the disclosed dart with a cotton or fibrous pellet inserted into the bore behind the loaded dart. However, Walker makes no provision for a detent to prevent premature sliding of the dart within the bore. Nor would the tranquilizer dart described by Walker exploit the full possibilities of substantial caliber reduction to provide a projectile with sufficiently high sectional density to confer substantial trajectory advantages for long range application. Instead, Walker's principle intention in including a sabot in the method of use seems to be to ensure adequate bore seal of the projectile. The type of cotton pellet sabot described, according to the specified method of use, would not function compatibly with very substantially reduced-caliber projectiles, particularly ones without affixed, substantially full caliber fins to form an interface to prevent blow-past of the sabot around or alongside the subprojectile. No mention is made of alternative embodiments which would employ sabots of reduced parasitic mass and friction and greater structural and dimensional uniformity. Nor are disclosed alternative embodiments to the tranquilizer dart suitable for general sporting applications including target shooting and hunting.
U.S. Pat. No. 632,838 to Jacobs does utilize round-shot projectiles which may be used at a substantial caliber reduction of shot-caliber relative bore-caliber. Spherical shot or pellets may exhibit higher sectional densities than are typical of many elongate full caliber fixed-piston blowgun projectiles. Even so, a spherical projectile, particularly in small shot-caliber sizes, is well recognized as having low sectional densities compared to equally calibered elongate solid-body ammunition. However, Jacobs does not disclose any way to use his blowgun to launch elongate subcaliber projectiles which could be more effectively adapted to exhibit high sectional densities in-flight. Instead, Jacob's principle intention is to exploit the convenience and economy of shot as a replacement for possibly more complex and expensive elongate projectiles such as darts. However, if small caliber shot such as BB shot were launched as full caliber projectiles, the correspondingly small barrel bore would excessively restrict the inflow of the user's breath. On the other hand, at larger caliber sizes, full caliber metal shot would generally be excessively massive for thrust provided by a user's breath. Thus, in order to utilize shot as a projectile source, Jacobs' blowgun exploits increased thrust-to-mass ratio by launching shot in an oversized bore with a full caliber carrier. However, the shot-retention lip and self-centering cavity of the carrier disclosed by Jacobs would not work effectively with elongate projectiles. The carrier's shot-retention lip may be considered as a type of projectile detent. Jacobs does not describe or contemplate any alternative detent means, such as an exterior magnetic detent, to hold the projectile in loaded disposition against the carrier, an arrangement which would allow the shot-retention lip to be eliminated and the cavity to be much smaller and shallower, thus facilitating the reduction of parasitic mass and bearing friction of the carrier. Such an arrangement would also eliminate the self-centering seating movement of the projectile within the carrier at launch initiation, thereby minimizing potential for vibration. Jacobs does not disclose any provision for engaging shot asymmetrically against the carrier, or for letting the shot-projectile ride directly on the bore, arrangements which would offer the possibility of requiring lessened carrier function, so that the nominal carrier might instead function primarily as a pusher plug, thereby offering additional opportunity to reduce the parasitic mass and friction of the carrier or pusher plug. Jacobs also does not disclose any provision to provide the bore with an interior guidance groove to apply enhanced guidance to the shot-projectile or other projectile during launch. Jacobs discloses a ported barrel and a cushioned stop to decelerate and retain the carrier at the completion of its power stroke. However, Jacobs does not describe or contemplate embodiments in which provision is made to engage and decelerate the carrier with a stop means or catching means that is not only yieldingly cushioned, but is also actually structurally displaceable relative the bore, in order to reduce potential of damage to the carrier and blowgun by exploiting conservation of momentum and inelastic collision to reduce the mutual impact shock of the carrier and the carrier stop upon each other. In the blowgun disclosed by Jacobs, the porting holes or slots needed to actuate partial carrier deceleration before reaching the carrier stop causes a shortening of the available power stroke length for a given bore length. Jacobs makes no provision for alternate embodiments in which the carrier may be replaced by, or embodied as, a launchable discarding sabot which is not retained in the bore after launch, thus not requiring in-bore deceleration, and therefore being able to exploit the longest possible power stroke for a given bore length to reach maximum launch velocity. Furthermore, such a discarding sabot might be more lightly structured than the retainable carrier disclosed by Jacobs, again facilitating reduction of parasitic mass and launch friction. Jacobs also discloses no provision for using bore rifling with pre-formed cooperating carrier surfaces to spin the carrier when launching spherical shot or other projectiles and thereby transferring stabilizing spin to the subprojectile.
Sabots generally work in a known manner to launch subcaliber projectiles, effectually decreasing the sectional density of a projectile during launch to achieve higher thrust-to-mass ratio, and by thereafter discarding, restoring a higher level of sectional density to the projectile for in-flight ballistic advantages and possible terminal ballistic advantages.
To achieve efficient and accurate launching of subcaliber projectiles, parasitic mass and bearing friction of the sabot must be kept within acceptable levels for available thrust. Suitable means must be utilized so that various other sources of resistance to launching, sabot disengagement, and sabot discarding are simultaneously limited to acceptable levels compatible with available thrust. Such means must still ensure secure locating of sabot projectile assembly components within the blowgun after loading, pending launch and during handling. Furthermore, to advantageously obtain higher efficiencies in terms of ballistic advantages, in-flight sectional density of the projectile must be made sufficiently high. The applicant knows of no prior-art blowgun able to simultaneously achieve or deliver all of these objects or advantages.
Prior-art blowguns were unable to efficiently launch subcaliber projectiles, and were therefore limited to effective use with full caliber projectiles. Full caliber projectiles, in order to be propelled by the relatively low operating pressures typically provided by a human user's breath, are required to have relatively low sectional densities, since a full caliber projectile with excessively high sectional density would be excessively massive for the available thrust and would thus be accelerated too slowly, achieving low exit velocities, poor trajectories, and probably causing discomfort or strain to the user's airways and lungs. The low sectional density and correspondingly low ballistic coefficients of full caliber blowgun projectiles means that their trajectories are excessively curved, particularly at extended ranges, making maximum range limited and causing targeting compensation at extended ranges to be very difficult due to the large amount of barrel elevation needed to compensate for the excessive amount of vertical drop of the projectile. Using full-caliber projectiles of lighter mass to achieve higher velocities and flattened trajectories may yield improved performance at close ranges, but at extended ranges trajectory will still be excessively curved, since lightening the mass but keeping the caliber constant results in even lower sectional density.
Another problem encountered with full caliber blowgun projectiles is a severe limitation in the ability to adjust projectile properties such as form factor, mass distribution, and configuration of aerodynamic surfaces, in order to improve aerodynamic performance and balance to yield benefits such as reduced drag, reduced sensitivity to cross-winds, increased ballistic coefficient, and improved stability and accuracy. This severe limitation is imposed by the requirement that some fixed portion of the projectile must be suitably shaped and sized to serve as a substantially full caliber piston slidingly sealable with the bore of the blowgun barrel.
Due to the problems set forth above, prior-art blowguns achieved only limited performance. Inadequate ability to improve projectiles in terms of characteristics such as sectional density, form factor, ballistic coefficient, mass distribution, balance, configuration of aerodynamic surfaces, and internal ballistic stability caused significant reduction of the benefits that were intended to be provided by prior-art attempts to improve performance. For example, prior-art strategies that yielded increased projectile velocity were able to provide flatter trajectories at short ranges, and modest increases in maximum range. However, the fact that full caliber projectiles still often had surprisingly low sectional densities and correspondingly poor ballistic coefficients meant that projectile velocity decreased very rapidly in flight, with the result that maximum range remained limited, and trajectories, particularly at extended ranges, remained excessively curved, so that long range targeting compensation was still very difficult due to excessive vertical drop of the projectile, while other problems included tendencies towards balance- and aerodynamic-related instability, along with various sources of inconsistency in the orientation and motion of the projectile as it was launched into flight. Additionally, the above problems with prior-art blowguns and projectiles tended to encourage methods of use which did not sufficiently customize blowguns and projectiles for each particular user's abilities, skills, and shooting objectives.
The problems discussed above would seem to make the blowgun a natural candidate for application of the solution or strategy of using subcaliber projectiles with associated sabot means. Subcaliber projectiles with associated discarding sabot means, which may also be referred to as sabot projectiles, have long been employed in various types of artillery and firearms, and provide greatly increased ability to adjust projectile properties such as form factor and mass, in order to obtain advantages such as, for example, higher thrust-to-mass ratio during launch acceleration, as well as improved sectional density and ballistic coefficient of the subcaliber projectile as it travels along its external trajectory. Such advantages in turn can provide performance improvements such as increased launch velocity, increased retention of velocity and energy downrange, reduced drag, flatter trajectory, increased maximum range, and more efficient target penetration.
However, despite the advantages described above, sabot projectile solutions have not been effectively employed in prior-art blowguns, due to the fact that prior-art sabot projectiles are not adapted to be launched efficiently within the range of operating pressures that may be typically provided by human breath. Furthermore, discarding of prior-art sabots does not operate efficiently within the range of velocities typically attainable by blowgun projectiles. Rather, successful prior-art sabot projectiles are generally designed to be used in firearms, artillery, and the like, in which the propellants employed to launch projectiles typically generate operating pressures which are measured in hundreds or thousands of pounds per square inch. The very tight fit between a sabot and a barrel bore necessary to form an adequate gas seal against such extremely high pressures of expanding propellant gases imposes very high levels of launching resistance as the sabot projectile assembly is pushed along the bore during launch. Furthermore, in firearms and artillery, projectile muzzle velocities typically approach or exceed the speed of sound, with correspondingly high levels of atmospheric drag encountered by the projectile. Such extremely high levels of operating pressures and in-flight drag are sufficient to overcome the high levels of launching resistance and discarding resistance imposed by the various types of connections or connecting means used in firearms and artillery for the purpose of securing sabot projectile components together and in correct position within the bore or firing chamber during various stages of the loading and launching sequence, while maintaining an adequate gas seal.
Sabots utilized in artillery are often somewhat structurally complex, especially if the subprojectile has a very substantial caliber reduction relative the bore caliber. Such sabots may have a carrier portion structurally separate from a pusher plug base portion. Some such carriers are one-piece, often with slots or other weakening zones to cause fracture into segments or pieces in a predictable manner upon launch. Such one-piece carriers are often formed by casting, using the subprojectile as a core in a casting mold, as in U.S. Pat. No. 4,360,954 to Burns et al. Other carriers may be multi-piece, often formed as several separate segments. Direct connections, or various types of intermediary connecting means, are employed to connect base to carrier, carrier segments to one another (where appropriate), and base and carrier to the subprojectile. Examples of such intermediary connecting means include frangible petals and severable spinner bands, as utilized respectively in U.S. Pat. Nos. 4,841,867 and 4,296,687 to Garrett. In order to disengage direct connections or intermediary connecting means between the sabot components and the subprojectile, artillery applications exploit high levels of inertial, compressive, and centrifugal forces, and of gas or air pressure loads, to cause obturation, upset, and other structural deformation, rupture, or fracture. For example, U.S. Pat. No. 5,297,492 to Buc utilizes propellant gas pressure entrapped in an internal aft cavity of the sabot to blow apart a solid obturator ring upon muzzle exit, while U.S. Pat. No. 4,735,148 to Holtman et al. exploits high air resistance pressure of in-flight drag and centrifugal forces generated by a projectile spin rate of approximately 45,000 rpm to shed and disintegrate a plastic composite sabot. In a related field, U.S. Pat. No. 5,239,930 to Adams et al. launched a hypervelocity subprojectile with a sabot that included a foam matrix projectile-retaining means, with the foam matrix crumbling into a powder under the immense linear acceleration forces of launch and thereby disengaging the sabot from the projectile. Forces generated during launch in artillery and hypervelocity projector applications are sufficient to overcome high levels of launching and discarding resistance of sabot projectiles. Even in the artillery sabot projectile adapted for launch from a smooth bore in U.S. Pat. No. 5,359,938 to Campoli et al, high operating pressures and high velocities are required to overcome high levels of launching, disengaging, and discarding resistance and to actuate the disclosed parallel lift separation method.
Such high levels of launching resistance and discarding resistance are not able to be overcome efficiently, if at all, by the much lower operating pressures provided by human breath, and by the considerably lower velocities and energies attainable by blowgun projectiles launched by human breath. Small arms sabot projectiles typically have a much less pronounced caliber reduction and are generally less complex than examples found in artillery applications. Small arms firearms typically employ sleeve or cup type sabots. Modified cup type sabots for small arms are often monolithic structures of molded plastic with multiple flexible petal segments extending from a pusher plug base. Such sabots often retain the subprojectile in place with a frictional fit, force-fit, interference fit or encapsulation. U.S. Pat. No. 6,073,560 to Stone utilized a small arms petalled sabot suitable for muzzle-loaders and other firearms, in which the weighted portions of the petals assisted in better exploiting centrifugal forces to open the sabot and expose greater area to air drag.
It may also be noted that some sabot projectiles used in firearms and artillery are able to exploit centrifugal force, produced by spin imparted by barrel rifling, in order to enhance the sabot's performance in peeling away from the projectile quickly and cleanly. However, it is problematic to apply barrel rifling to blowguns without excessively increasing launching resistance. Also, blowgun rifling would typically launch projectiles with slower spin rates than those imparted to firearm projectiles, yielding relatively low levels of centrifugal force to be exploited to aid discarding.
An example of a small arms sabot that did not rely on centrifugal force is U.S. Pat. No. 4,434,718 to Kopsch et al., which utilized a sabot projectile that included a sabot and finned subcaliber projectile suitable for launch from a shotgun cartridge through and from a smooth bore barrel. The sabot is a simple, cylindrical shell or can type, with long thin petals designed to be opened by air pressure. The finned subprojectile has fins offset to produce aerodynamically induced stabilizing spin. It is not explicitly stated how the subprojectile is dispositioned when loaded within the cylindrical sabot other than that the backs of the fins are supported on the transverse metal disk. However, taking into consideration the accompanying drawing illustrations, it appears that the intention is for the fins to fit snugly against the petals when the sabot is loaded within the shotgun cartridge case, holding the sabot body in an essentially centered position axisymmetric with the sabot cylinder. Certainly that seems the only method that would not require additional complexity, or extra mass. The crimped forward end of the cartridge shell serves as an additional or alternative projectile retaining means prior to launch. Stone's sabot projectile cited above does not require a cartridge shell when used in a muzzle-loader.
It may be useful to summarize several situations likely to result if prior-art sabot projectiles were used or superficially adapted for use in a blowgun, even relatively simple small arms types such as those in the above cited U.S. Pat. Nos. 4,434,718 and 6,073,560. First, inadequate operating pressures to overcome launch resistance would result in the sabot projectile either being stuck in the barrel bore, or else exiting the barrel bore with reduced velocity. Second, in the event the sabot projectile did attain satisfactory exit velocity, since satisfactory velocities for blowgun projectiles are still typically too low to actuate discarding of prior-art sabots, there would likely be a failure of the sabot to achieve separation and thereby discard, in which case the sabot means and the subcaliber projectile would continue to travel along an external trajectory together, performing in effect as a full caliber projectile and causing the subcaliber projectile to fail to achieve its true function. Even if separation occurred, release would likely not be quick and clean, thus transmitting excessive drag from the sabot means to the subcaliber projectile during discarding, thereby lowering projectile velocity, or introducing trajectory inaccuracies for the projectile, or both. Third, even if the degree of discarding resistance were lowered sufficiently to guarantee successful, clean discarding of the sabot means, the consequent looseness or tenuousness of the connection between the sabot means and the projectile proper would almost certainly result in premature separation of the sabot projectile components prior to launch acceleration or prior to exit from the barrel bore. This summary also indicates a list of pitfalls that should preferably be avoided by a successful solution to providing a blowgun that can efficiently and accurately launch subcaliber projectiles.
It will be apparent to one familiar with the art that even the airgun-compatible sabot utilized in U.S. Pat. No. 5,150,909 to Fitzwater would not operate successfully or efficiently at pressures provided by human breath. Nor would the sabots utilized in U.S. Pat. No. 422,347 to Hyde and U.S. Pat. No. 3,536,054 to Stephens et al., even though they are designed for use in vacuum cannons, which operate at modest pressure differentials. Blowgun pressure differentials, however, are generally even more modest, probably never or rarely exceeding 4 pounds per square inch (psi), with 2 psi and lower being much more typical for the average user.
One other blowgun-related patent to be considered is U.S. Pat. No. 4,854,294 to Lala, which disclosed a pressure-assisted blowgun in which there was no direct connection between the mouthpiece and the blowgun tube; rather a breath operated valve was used to connect a source of pressurized gas at 120 psi to the blowgun tube to launch target darts of 10 to 15 grains. Although nominally a blowgun, Lala's apparatus does not utilize the user's breath to propel the projectile, but merely to actuate a pressure valve connected to an external pressure source. Such a solution may not appeal to those blowgun users who prefer to use their own breath to provide the motive force to accelerate and launch the projectile, rather than rely on an external motive source such as a canister of pressurized gas. It may also be appreciated that 10 to 15 grain target darts, which are typical masses for commercial wire rod darts used with popular 40 caliber and 50 caliber blowguns, would have very low sectional densities, even lower than that of a steel BB shot used in mechanical airguns. Lala does not disclose, describe, or contemplate any alternative embodiments capable of launching subcaliber projectiles.
It should be emphasized how important it is, in certain embodiments, that when the sabot projectile assembly has completed exiting the bore through the muzzle opening of the blowgun barrel, and the propulsive thrust has consequently substantially dissipated, there should preferably at that time be, as nearly as possible, substantially no positive connection between the subcaliber projectile and the sabot means, either directly or via intermediary connecting means, as would provide any substantial resistance to axial displacement of the subcaliber projectile forwardly relative the sabot means, nor to axial displacement of the sabot means rearwardly relative the subcaliber projectile. This point is very important, because at the relatively low velocities and energies which blowgun projectiles typically attain, it may be surprisingly difficult to obtain separation, or clean separation, of the sabot from the subcaliber projectile if there is even a seemingly tenuous connection between the two components which would excessively resist the type of relative axial displacement described in the preceding sentence. Thus, there is the potential for even a seemingly weak force-fit engagement, frictional engagement, or the like, to be able to either cause failure of the sabot to separate at all or else cause sabot separation to either be too slow or too violent, thereby transmitting drag or trajectory inaccuracies or both to the projectile proper.
It is therefore adviseable to minimize or eliminate the need for positive connectios or connecting means between sabot projectile elements by, for example, utilizing some type of external detent such as a magnetic detent. As was seen, closely related blowgun patents did not utilize a detent to locate elements of a sabot projectile in disposition pending launch. A number of patents in other fields utilize magnetic means to retain a projectile in loaded desposition pending launch. Examples include U.S. Pat. No. 3,463,136 to Vadas et al., U.S. Pat. No. 3,142,294 to Baldwin, and U.S. Pat. No. 2,293,957 to Wells, all of which disclosed mechanical air guns that utilized a magnetic bolt or magnetic breech pin to hold a BB shot or other magnetically attactable full caliber airgun projectile in loaded position pending launch pressurization. U.S. Pat. No. 4,860,719 to Scheiterlein utilized a magnetic hold-down device for holding an arrow securely on the arrowrest of a crossbow without direct contact of the hold-down device with the arrow or arrowhead. However, none of these patents disclose alternate embodiments or methods of use in which such a magnetic bolt, breech pin, or hold-down device is used to locate an element of a sabot projectile assembly preparatory to firing; and in particular to hold a subcaliber projectile in place against, within, or in front of a sabot means in loaded disposition pending launch.
It is also important to note that, despite the seemingly superadequate operating pressures and projectile velocities available to overcome launching resistance and to actuate sabot discarding in firearms and artillery, a survey of certain prior art designs of firearm and artillery sabot projectiles reveals concerns for minimizing adverse effects on projectile trajectory and accuracy that may be caused during sabot discarding. For example, U.S. Pat. No. 5,481,980 to Engel et al utilized special parting plane geometry to avoid impact of edges of the sabot segments upon the projectile during sabot separation. U.S. Pat. No. 4,841,867 to Garrett used a sabot base free of direct positive coupling to the subprojectile so as to provide a more compatible interface of the base with the gun barrel. If such concerns for providing cleaner sabot release and separation are deemed worthy of attention in adapting sabot projectiles for use in firearms or artillery, they may be considered as even more critical in obtaining optimal, or even satisfactory, performance from a sabot projectile adapted for use in a blowgun.
Another limiting factor in the performance of prior art blowguns is that insufficient correctional guidance is applied to certain portions of the projectile during launch acceleration, resulting in internal ballistic instability that translates into accuracy dispersions in the projectile's external trajectory. Certain prior art designs attempted to address this problem, but the means employed resulted in increased launch resistance, increased projectile mass, and undesirable aerodynamic and balance characteristics of the projectile. This may be seen in the cylindrical bodied darts utilized in U.S. Pat. No. 3,735,748 to Gaylord, in which the cylindrical piston bodies are intended to align the dart, including the forwardly extending rod, coincident with the longitudinal axis of the barrel bore. However, many typical commercial blowgun darts do not utilize a cylindrical piston body, but rather a piston body that is essentially conical, and which usually does not maintain the longitudinal axis of the dart in alignment with the longitudinal axis of the barrel bore. In a typical full caliber blowgun projectile, the forward end or tip of the projectile, which is often the forward tip of a slender rod, is usually the only point of direct contact between the bore and the often relatively rigid rod, since the rod typically angles down from a point of substantially rigid attachment with, or insertion into, a full caliber fixed piston, to rest upon the bore. Since the forward tip of the rod is usually the rod's only direct point of contact with the bore, the rod is provided with only a very small area of direct support contact with the bore, and thus very minimal guidance is applied to the forward end of the rod, which is also the forward end of the projectile. This arrangement, in conjunction with the typically slightly loose fit of the piston within the bore, usually necessary in a blowgun projectile to avoid excessive friction and launching resistance, leaves some play in the orientation of the dart. Particularly, the forward tip of the rod may slide transversely upon the bore and swing toward the left or right, or possibly even oscillate between left and right. The forward tip of the rod may also lift off the bore, due to play of the piston under launch pressure, or due to barrel curvature, such as that caused by gravity-induced sag, in which case substantially no guidance is applied to the forward end of the rod unless contact with the bore is reestablished essentially by happenstance.
Prior art blowguns also presented certain disadvantages concerned with target shooting. Prior art practices for shooting blowgun projectiles at targets and retrieving projectiles from the targets suffered from an excessively high potential for damage to projectiles, which are typically intended to be reusable, and from excessive amounts of time and effort spent in retrieving projectiles from the target after a round of shooting. Prior art practices also placed limitations on accuracy of assessment of shot placement on the target face, and made it difficult to practice more than a rather narrow variety of target practice shooting styles and formats.
Prior art blowguns also presented problems in launching spherical projectiles, and certain other essentially non-elongate projectiles, since full caliber spherical projectiles typically had relatively high sectional densities and poor air seal performance, resulting in poor launch acceleration and reduced velocities.